l propose to develop an animal system for the study of hormonal control of rapid changes in reproductive behaviors that occur in response to social conditions. The frog, Acris crepitans, is an ideal model in that 1) individuals can switch rapidly between discrete categories of mating behaviors, 2) behavioral switching can be experimentally induced through playbacks of calls of larger males, and 3) behavioral and hormonal studies can be performed under natural conditions. The goals of this series of studies are threefold. The first is to discover whether a previously determined correlation between intrasexual variation in mating behavior with the neuropeptide arginine vasotocin (AVT) reflects a causal interaction (i.e. do changes in AVT control rapid changes in mating behavior?). This will be accomplished using hormonal manipulations under natural conditions. The second is to examine brain hormonal changes (using immunocytochemistry and image analysis) in response to social interactions represented by acoustic signals of both dominant and subordinate individuals. The third is to begin examining the role of steroid hormones in rapid changes in mating behavior by measuring steroid levels using radioimmunoassays and, if time permits, by manipulating steroid levels. These studies will aid in our understanding of potential hormonal mechanisms involved in controlling intrasexual variation in vertebrate behavior, as well as how social conditions may influence reproductive' behaviors in individuals through effects on hormonal systems within the brain. Neuropeptide studies of non-humans have provided exciting information on hormonal involvement if social interactions, but as yet, many aspects of this remain poorly understood. The proposed studies can provide predictive models that may be used to evaluate biochemically based reproductive disorders in humans.